This paper aimed to investigate the biodiesel degradation characteristics under different storage conditions. The qualities of twelve biodiesel samples, which were divided into 3 groups and stored at different temperatures and environments, were monitored at regular interval over a period of 52 weeks. Experimental results demonstrated that the biodiesel under test degraded less than 10% within 52 weeks for those samples stored at 4 and 20 degrees C while nearly 40% degradation was found for those samples stored at a higher temperature, i.e. 40 degrees C. The results suggested that high temperature, together with air exposure, greatly increase the biodiesel degradation rate. The temperature or air exposure alone, however, had little effect on biodiesel degradation. Water content in biodiesel will enhance biodiesel degradation due to hydrolysis but its effect is much less than the above two factors. (c) 2005 Elsevier Ltd. All rights reserved.